Porcine proliferative enteropathy (PPE or PE), also referred to as Ileitis, is one of the most economically burdensome diseases of the swine industry. The disease has been reported to affect 12% to 50% of pigs on farms world-wide (Diseases of Swine, 7th Edition, 560-569 (1992)). Although the economic impact of PPE is felt largely by the swine industry, the disease has also been shown to affect multiple mammalian species, including monkey, rabbit, hamster, horse, ostrich, fox, ferret, rat and emu (Diseases of Swine, 7th Edition, 560-569 (1992)). In animals exhibiting proliferative hemorrhagic enteropathy (PHE), the acute form of PPE, the death rate is as high as 50 percent, and pregnant animals infected often abort within the first 6 days (Diseases of Swine, 7th Edition, 560-569 (1992)). The causative agent for PPE was first determined and isolated by Lawson et al. (Journal of Clinical Microbiology 31(5):1136, (May 1993)). The bacteria isolated by Lawson et al. were obligate, intracellular, gram-negative curved rods which tolerated oxygen only at reduced pressure from atmospheric tension and grew in vivo only in enterocytes. Lawson et al. isolated two strains of the bacteria and deposited them as NCTC 12656 and NCTC 12657.
Further phylogenetic characterization and naming of these bacteria was performed by McOrist et al. (International Journal of Systematic Bacteriology, 45(4):820-825, (October 1995)). The causative agent of PPE was determined to be the obligate intracellular bacterium, originally found by Lawson et al., now designated Lawsonia intracellularis (LI). This organism is a gram-negative, flagellated bacterium that infects immature epithelial cells of the intestinal crypts, called enterocytes.
In the early stages of infection, the bacterium associates with the cell membrane and quickly enters the crypt epithelial cells via an entry vacuole (McOrist, S., et al., The Canadian Journal of Veterinary Research, 70(2):155-159, (April 2006)). This vacuole rapidly breaks down and the bacteria flourish and multiply freely in the cell cytoplasm. One of the distinguishing features of this disease is the uncontrollable proliferation of crypt epithelial cells which results in thickening of the mucosal lining of the small, and sometimes the large, intestine. In pigs, infection with LI causes diarrhea, stunted growth and in some cases sudden death.
Proliferative enteropathies are a group of diseases with widely differing appearances and symptoms, one member of which is PPE (Diseases of Swine, 7th Edition, 560-569 (1992)). Several different forms of PPE (acute, chronic, necrotic and subclinical) can also be distinguished; however they all have the common underlying pathogenic cause being Lawsonia intracellularis. The disease initially develops as a progressive proliferation of the immature intestinal epithelial cells which are infected by Lawsonia intracellularis. This form of the disease is characterized by the presence of bloody or blood-tinged diarrhea, blood clots and sudden death. Porcine intestinal adenomatosis (PIA) is considered the chronic and most common form of the disease, which is seen in growing pigs (nursery to late finishing stage). Proliferative hemorrhagic enteropathy (PHE) is considered the acute form of the diseases, affecting the terminal ileum and colon of adult pigs (4-12 months of age). PHE develops from PIA and is distinguished by severe bleeding into the lumen of the intestine from the pre-existing PIA lesions. This form of the disease is observed in the terminal ileum and upper part of the proximal colon and is characterized by extensive thickening of the mucosal lining of the affected areas with little or no inflammation in the mucosal surface. Necrotic enteritis is another form of the disease, which is characterized by severe thickening of the ileum along with presence of yellowish necrotic lesions in the ileum. Another form of the disease that has been described in pigs with Lawsonia infections is a subclinical disease producing carrier animals without overt signs of disease.
Growth of Lawsonia intracellularis in cell culture requires an environment that contains an unusual gas mixture (oxygen, carbon dioxide, nitrogen and hydrogen). In addition, the bacteria do not display observable cytopathic effects in the host cells. These factors underscore the importance of researching unconventional technologies in order to develop efficacious vaccines to protect against the disease caused by Lawsonia, but which do not require the cultivation of the bacteria. One such approach involves the application of recombinant DNA technology to develop a subunit vaccine. Previous studies have utilized ARTEMIS and TB-parse to annotate the fully sequenced Lawsonia genome (US2006/0024696).
Despite these advances, development of subunit vaccines has been hampered by the lack of information on the identity of protective antigens that can be used as the basis for a vaccine. The present invention addresses these and other needs.
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